1. Field of the Invention
The present invention relates to a ground fault interrupter and more particularly to a multiple-pole circuit breaker having ground fault detection circuitry which includes a single trip solenoid with multiple windings.
2. Description of the Prior Art
Ground fault interrupters are generally known in the art. Examples of such devices are disclosed in U.S. Pat. Nos. 3,852,642; 3,999,103; 4,015,169; 4,081,852 and 4,208,688, assigned to the same assignee as the present invention, hereby incorporated by reference. Ground fault interrupters are typically used for personnel protection against ground faults near swimming pools, marinas, outdoor receptacles and the like.
Such devices include single and multiple-pole circuit breakers which include one or more pairs of separable main contacts actuated by an operating mechanism, responsive to thermal and magnetic tripping means for tripping the separable main contacts during overload and short circuit conditions. An example of a single-pole ground fault interrupter is disclosed in U.S. Pat. No. 4,081,852. Examples of multiple-pole circuit breakers are disclosed in U.S. Pat. Nos. 3,999,103; 4,015,169 and 4,208,688. Ground fault detection circuitry is also incorporated to form a ground fault interrupter to additionally trip the separable main contacts during a ground fault condition at electrical current levels substantially less than the threshold tripping levels of the thermal and magnetic tripping means to prevent personnel hazards attendant to ground faults.
The ground fault detection circuitry typically includes a current monitor, such as differential transformer, for monitoring any current imbalance between the line conductors and the neutral conductor, indicative of a ground fault, an amplifier and a shunt trip. The differential transformer normally includes one or more a toroids with secondary windings. The line and neutral conductors are passed through the core of the toroid. During normal conditions, the current through the line and neutral conductors generates equal and opposite magnetic fields which cancel and thus do not induce a voltage in the secondary winding of the toroid. However, in the event of a ground fault, the electrical current in the line and neutral conductors is unequal causing a resultant magnetic field which induces a voltage in the secondary winding of the toroid, which, in turn, is amplified and utilized to actuate the shunt trip to trip the circuit breaker separable main contacts.
In the event of a ground fault condition, all of the poles of the circuit breaker are tripped concurrently by the shunt trip, which generally consists of a plurality of trip solenoids with reciprocally mounted plungers interlocked with the circuit breaker operating mechanisms for each pole. More specifically, one trip solenoid is provided for each pole and interlocked with the operating mechanism for that pole. Mechanical interlocking is also provided between the poles to trip all of the poles concurrently.
Ground fault interrupters are disposed in an insulated housing, adapted to be received in a standard circuit breaker panelboard. The housing is formed with side-by-side compartments, separated by partition walls. The circuit breaker components (e.g., main contacts and operating mechanisms) are disposed in one or more of the compartments while the ground fault detection and trip circuitry are disposed in the balance of the compartments. In known multiple-pole ground fault interrupters, the trip solenoids for each pole are disposed in a separate compartments due to their size. Therefore, a two pole ground fault interrupter generally requires four compartments. The circuit breaker components are disposed in two compartments while the trip solenoids for both poles as well as the balance of ground fault detection circuitry are disposed in the other two compartments.
Since the trip solenoids are disposed in different compartments, interconnection wiring must be provided between the compartments. In some known ground fault interrupters, such as the ground fault interrupters disclosed in U.S. Pat. No. 3,999,103, such interconnecting wiring is done by hand which increases the labor cost to manufacture the device. More specifically, in such ground fault interrupters, the ground fault detection circuitry used to actuate the trip solenoids is generally formed from discrete electrical components that are hand soldered with appropriate interconnections made between compartments for the trip solenoids. Such hand wiring and soldering results in relatively high labor costs to manufacture the device. Moreover, such assembly results in relatively tightly compacted compartments which further adds to the labor time to assemble the device.